Means for governing the pressure in ventilating units



March 3, 1965 s. MATTS ETAL 3,174,507

MEANS FOR GOVERNING THE PRESSURE IN VENTILATING UNITS Filed Aug. 23. 1962 7 fi---v I? l l I i I /0 I L b k l I r, j L 9 5 I S United States Patent M MEANS FOR GOVERNING TI E PRESSURE IN VENTILATING UNITS Sigvard Matts, Farsta, and Bruno Ekeiund, Gothenburg,

Sweden, assignors to Ahtiebolaget Svenska Flahtfahriiten, Stockholm, Sweden Filed Aug. 23, 1%2, Ser. No. 219,052 2 Claims. (Cl. 137565) The present invention relates to a device in a distribution duct connected to a fan for maintaining constant the static pressure near two or several air outlets adjusted by means of dampers and located at a relatively large distance from the fan, which device consists of a pressure sensitive means and an adjustment device governed by said means.

Arrangements for the adjustment of the pressure in air ducts comprising parts of ventilating units were previously known. In such units a number of consumption points equipped with dampers are often located at a considerable distance from a central apparatus room, where the fan of the unit and devices for the governing of the fan are located. These devices may be intended for the adjustment of guide rails or return dampers or as speed control means for the fan motor. It is customary to govern such a ventilating unit with the aid of a manostat or pressure responsive device attached to the consumption end of the ventilating plant.

It is, of course, impossible to maintain constant the pressure in front of each consumption damper for each combination of different damper positions only with the aid of the adjustment device of the fan, but it is possible to place the manostat so that the variations become moderate in front of all the dampers. Often one cannot, however, beforehand accurately determine the distribution of the consumption between the dififerent dampers. Therefore, one cannot predetermine the best placing of the manostat. In an accurate planning work one must, therefore, make tests in the completed unit by moving the manostat from one position to another. It is thereby often shown that the best possible place from adjustment viewpoint is difiicult to get at from practical viewpoints. Furthermore, diflicult changes are required in the location of the necessary pipes from the manostat to the apparatus room.

The present invention, the object of which is to eliminate the drawbacks in previously known arrangements of this kind, is characterized in that the pressure sensitive means is connected to an extra, relatively small branch duct arranged close to the fan outlet and that in this branch duct are attached a throttling flange arranged before the opening to the pressure sensitive means, said throttling flange having a pressure-fall characteristic similar to that of the distribution duct up to the said opening and also an adjustment damper placed in the outlet of the extra branch duct, which damper is arranged to be affected by said pressure sensitive means via the adjustment device for the fan, so that the position of this adjustment damper will constantly substantially correspond to the average position of the dampers of the air outlets.

The invention will now be described more in detail with reference to the accompanying drawing which schematically shows a ventilating unit with an exemplifying embodiment of a device in accordance with the invention.

In the schematic drawing 1 designates the consumption end of a distribution duct 3 connected to a fan 2. This is equipped with one or several damper-adjusted air outlets, for instance 4 and 5. 12 indicates an adjustment device for varying of the capacity of the fan 2. 6 indicates a pressure sensitive means and 7 indicates a servo- 3,174,507 Patented Mar. 23, 1965 motor controlled by the said pressure sensitive means. In accordance with the invention the pressure sensitive means 6 is connected to a branch duct 3' arranged at the fan outlet. The branch duct is equipped with a throttling flange 9 arranged before the opening 8 of the pressure sen sitive means 6, said flange having a pressure-fall characteristic corresponding approximately to that of the distribution duct 3 and also with an adjustment damper 11 placed at the outlet 10. The damper 11 and the adjustment device 12 are governed together by said pressure sensitive means 6 via the servo-motor 7. Each combination of the positions of dampers of the air outlets corresponds to a certain total air consumption. If this total consumption is small, i.e., if the air outlet dampers on an average are almost closed, the fan 2 must be throttled by means of the adjustment device 12 in order that the pressure P in the consumption end shall not rise. If the total consumption is large, i.e., if on an average the air-outlet dampers are almost open, the fan capacity must be increased in order that the pressure P shall not fall. This means that each position of the adjustment device 12 corresponds to a certain average position for the air outlet dampers. By connecting the adjustment device 12 with the adjustment damper 11 in a suitable way it will then obtain a position corresponding to the average position of the dampers of the air outlets. Since the throttling flange 9 has a pressure fall characteristic which corresponds to that of the duct 3, the pressure P will thus be substantially equal to the pressure P The same effect will then be obtained with the manostat connected to P as if it was connected to P P can accordingly be maintained approximately constant in spite of the fact that the pressure sensitive means is placed in immediate proximity to the fan, for instance in the apparatus room for the fan and its adjustment devices. By changing the throttling flange ii somewhat the position for the constant pressure P; can be moved towards that of the air outlets without the need to move the manostat. Besides a simplified installation, also increased trimming possibilities are hereby gained according to the invention.

In operation, the throttling flange 9 in the small branch duct 3' functions to cause a pressure change which is substantially equal to that in the main duct up to a point near the air outletthe point at which the sensing means of hitherto pressure regulating devices were disposed. The adjustment damper 11 functions to cause a pressure change which is substantially equal to the mean pressure change of the air outlets in their actual positions. It is, therefore, evident that the adjustment damper performs a function supplemental to that of the orifice of the throttling flange.

As pointed out earlier, each combination of the positions of the dampers in the main air outlets corresponds to a certain total air consumption and a certain air flow in the main duct. If some of the main dampers are closed, for example, the air flow in the main duct decreases and this causes a corresponding increase in the static pressure in the main duct and in the small branch duct, whereupon the pressure responsive device 8, 6 in the small duct will sense the increase in pressure and will act through the servo-device 7 to decrease the output of blower fan 2 until the prior static pressure in the main duct is substantially restored.

However, the pressure increase in the small branch duct would not quite follow the pressure increase in the main duct because the resistance to air flow by the adjustment damper 11if not adjusted-would not correspond to pressure increase caused by the changed condition of the dampers in the main air outlets. In order to compensate for the changed condition of the main dampers the adjustment damper 11 needs to be correspondingly a changed to a more closed position. This adjustment of the damper 11 is made by the action of the pressure sensing device 6 and the servo-device 7 simultaneously with the adjustment of the blower fan output. Thus even through damper 11 tends to close, P drops to correspond to the decrease in pressure caused by the decrease in fan speed.

Since each combination of positions of the main outlet dampers corresponds to a certain air flow, which, in turn, corresponds to a certain position of the blower control device, the adjustment of the damper 11 can be regulated by the same device which controls the blower.

What we claim is:

1. Apparatus for regulating the static pressure in a ventilating air duct system having a relatively long main duct connected to a motor driven air supply blower and having a number of branch ducts with damper regulated air outlets disposed at the outer end of the main duct, comprising, in combination, a relatively small control branch duct connected to said main duct near the blower in a manner to be responsive to static pressure in said main duct and having an air outlet at its outer end, a throttling flange arranged in said control branch duct which is constructed and arranged to cause a pressure drop in said control branch duct which is substantially equivalent to the pressure drop in the main duct up to a predetermined point near said air outlets, an adjustment damper in said control branch duct located at a distance downstream of said throttling flange to provide between them a pressure control chamber, pressure sensing means connected to said pressure control chamber and responsive to the static pressure therein, a servodevice operatively connected to said pressure sensing means, a control device responsive to said servo-device arranged to regulate the speed of said blower and to change the position of said adjustment damper in such manner that it will cause a pressure change substantially equal to the actual mean pressure change in the main duct caused by the dampers to the branch duct air outlets.

2. Apparatus for regulating the static pressure in a ventilating air duct system having a relatively long main duct connected to a motor driven air supply blower and having a number of branch ducts with damper regulated air outlets disposed at the outer end of the main duct, comprising, in combination, a relatively small control branch duct connected to said main duct near the blower in a manner to be responsive to static pressure in said main duct and having an air outlet at its outer end, a throttling flange arranged in said control branch duct which is constructed and arranged to cause a pressure drop in said control branch duct which is substantially equivalent to the pressure drop in the main duct up to a predetermined point near said air outlets, an adjustment damper in said control branch duct located at a distance downstream of said throttling flange to provide between them a pressure control chamber, pressure sensing means connected to said pressure control chamber and responsive to the static pressure therein, and means responsive to said pressure sensing means constructed and arranged to regulate the speed of said blower and to correspondingly change the position of said adjustment damper to compensate for the mean change in condition of the dampers in said branch ducts.

References Cited by the Examiner UNITED STATES PATENTS 2,896,850 7/50 Ashley 236-92 M. CARY NELSON, Primary Examiner.

ISADOR WEIL, MARTIN P. SCHWADRON,

Examiners. 

1. APPARATUS FOR REGULATING THE STATIC PRESSURE IN A VENTILATING AIR DUCT SYSTEM HAVING A RELATIVELY LONG MAIN DUCT CONNECTED TO A MOTOR DRIVEN AIR SUPPLY BLOWER AND HAVING A NUMBER OF BRANCH DUCTS WITH DAMPER REGULATED AIR OUTLETS DISPOSED AT THE OUTER END OF THE MAIN DUCT, COMPRISING, IN COMBINATION, A RELATIVELY SMALL CONTROL BRANCH DUCT CONNECTED TO SAID MAIN DUCT NEAR THE BLOWER IN A MANNER TO BE RESPONSIVE TO STATIC PRESSURE IN SAID MAIN DUCT AND HAVING AN AIR OUTLET AT ITS OUTER END, A THROTTLING FLANGE ARRANGED IN SAID CONTROL BRANCH DUCT WHICH IS CONSTRUCTED AND ARRANGED TO CAUSE A PRESSURE DROP IN CONTROL BRANCH DUCT WHICH IS SUBTANTIALLY EQUIVALENT TO THE PRESSURE DROP IN THE MAIN DUCT UP TO A PREDETERMINED POINT NEAR SAID AIR OUTLETS, AN ADJUSTMENT DAMPER IN SAID CONTROL BRANCH DUCT LOCATED AT A DISTANCE DOWNSTREAM OF SAID THROTTLING FLANGE TO PROVIDE BETWEEN THEM PRESSURE CONTROL CHAMBER, PRESSURE SENSING MEANS CONNECTED TO SAID PRESSURE CONTROL CHAMBER 